P&S Journal: Spring 1996, Vol.16, No.2
Study Finds Syndrome X has Physiological Basis
Researchers have discovered evidence that Syndrome X has a physiological basis in a study that also casts doubt on the superiority of angiography as a diagnostic tool.
People with Syndrome X experience angina in response to exercise or stress. While they have abnormal exercise stress tests-suggesting the presence of an anomaly in the coronary arteries-they have normal angiograms, suggesting just the opposite. Physicians have been at a loss to explain these contradictory findings, leading some to speculate that the syndrome is psychological in origin.
However, a P&S study published last year in the Journal of the American College of Cardiology provides new evidence that Syndrome X has a physiological basis. In the study, 30 patients with the classic findings of Syndrome X (chest pain, abnormal stress tests, and normal angiograms) were examined using intravascular ultrasound, which is more sensitive than angiography. A miniaturized probe was threaded directly inside the coronary arteries, and images were retrieved from patients both at rest and during exercise. "We found abnormalities of two kinds," reports study leader Dr. Mark Apfelbaum, assistant professor of clinical medicine. "About a third of the patients had significant focal deposits of plaque." The irregularly shaped artery-clogging deposits are hard to detect with angiography "unless the camera is angled just right," says Dr. Apfelbaum.
In another third of the patients, ultrasound imaging revealed marked thickening of the inner walls of the coronary arteries, a finding not found through angiography. Mild thickening is a common consequence of aging, but it usually occurs in combination with atherosclerotic plaques. Significant thickening in the absence of atherosclerosis is seen commonly in transplant patients, Dr. Apfelbaum reports. "This unexpected finding is intriguing and warrants further study."
Because of the new findings, Dr. Apfelbaum says, "the angiogram may not be as gold a standard as we have always thought it to be. In both of these groups, the response to exercise was abnormal. They had very substantial rises in heart rate. Instead of dilating, their arteries constricted. So, both anatomically and physiologically, the coronary arteries were not normal."
The remaining third of the patients had normal coronary arteries on intravascular ultrasound and normal response to exercise. "Interestingly, most of those patients had had conventional stress tests," says Dr. Apfelbaum. Patients with abnormal ultrasounds had more sophisticated stress tests, with thallium or echocardiographic imaging, leading researchers to conclude that advanced stress tests are much more reliable indicators of coronary artery abnormalities.
"To get the full picture, patients who have chest pain and an abnormal exercise test should have an intravascular ultrasound," says Dr. Apfelbaum. "It can be done at the same time as the angiogram. It adds another 30 minutes and a tiny additional risk."
These findings should offer some comfort to the tens of thousands of people who have been diagnosed with Syndrome X. "Some of these people truly are normal and do not need to be on therapy. We can now reassure them that nothing terrible is going to happen to them, and we don't think their heart is the problem."
Patients with abnormal arteries discovered by ultrasound and abnormal exercise tests probably do have early coronary artery disease, he adds. "First, and certainly not least, we can tell them we do have a diagnosis. We should put these people on antianginal therapy, plus aspirin, if there's no contraindication, as a precaution against coronary artery disease. Fortunately, the prognosis for such patients is very good."